The project on PVR Tg21 mice in comparison with the monkey neurovirulence test of OPV has been continued. Some tests in monkeys were carried out with Types 2 and 3. With Type 3 OPV a number of tests in Tg mice were repeated to establish reproducibility of results and variabilities. Coordination of the WHO Study and assistance given by our lab to other participants of the Study enabled the completion of the exploratory stage of the Study with statistically reliable results on Type 3 OPV: PVR Tg21 mice discriminated between 'good' and 'bad' vaccines. The same positive data were obtained by our lab with type 2 OPV. The data were reported to WHO in March '95, and a second year grant awarded. Results of the USA - Japan collaboration were presented at the ICLAS meeting in July '95.